Silence uninitialized variable compiler warning in sepgsql

At -Og optimization gcc warns that variable tclass may be used
uninitialized when relkind == RELKIND_INDEX. Actually that can't
happen due to an early return, but quiet the compiler by initializing
tclass to 0.

In passing, use uint16_t consistently for the declaration of tclass.

Complaint and initial patch by Mike Palmiotto. Editorializing by me.
Probably not worth backpatching given that it is cosmetic, so apply
to development head only.

Discussion: https://postgr.es/m/flat/623bcaae-112e-ced0-8c22-a84f75ae0c53%40joeconway.com

contrib/sepgsql/relation.c

@@ -243,7 +243,7 @@ sepgsql_relation_post_create(Oid relOid)
 	HeapTuple	tuple;
 	Form_pg_class classForm;
 	ObjectAddress object;
-	uint16		tclass;
+	uint16_t	tclass;
 	char	   *scontext;		/* subject */
 	char	   *tcontext;		/* schema */
 	char	   *rcontext;		/* relation */
@@ -413,7 +413,7 @@ sepgsql_relation_drop(Oid relOid)
 {
 	ObjectAddress object;
 	char	   *audit_name;
-	uint16_t	tclass;
+	uint16_t	tclass = 0;
 	char		relkind;
 
 	relkind = get_rel_relkind(relOid);